Two separate projects are proposed, one on channel selectivity, and the other channel gating. Our current major goal is to develop a molecular theory that will account for nerve excitability. We will study sodium channel ionic currents, gating currents, and current fluctuations in a frog node treated with sea anemonae toxin to slow sodium inactivation. The quantitative theory treats membrane channel proteins that are envisioned as taking on several conformational states, one of which is associated with the open channel; the membrane electric field drives the protein to its open conformation through interactions of the field with protein dipole moments associated with the various conformational states. The theory will be tested by estimating constants from ionic current data, and then using these constants to predict gating currents and the covariance function for the current fluctuations. We also are recording from single sodium channels to exploit advantages inherent in studies of individual (or small groups of) molecules. These experiments use cultured rat myotubes.